The subject matter disclosed herein relates generally to mechanical turbines, and more particularly to a system and method for providing compliant rotating seals.
Mechanical turbines, such as gas or steam turbines, include numerous surfaces that include seals, for example, to reduce or prevent the undesired escape of combusted gases or steam. A particularly challenging form of these seals are those that seal a moving or rotating surface (e.g., with respect to a stationary surface). For example, turbines include rotating surfaces, such as shafts, rotors, etc., that include seals between them and adjacent stationary surfaces, such as stators, shrouds, etc. Labyrinth seals are a popular form of rotating seals for this purpose that include closely mating portions (e.g., straight-threaded extensions or “teeth” that are stationary and/or moving during operation) that mechanically repel the flow of gas or fluid by creating an effective obstacle path that is further enhanced by centrifugal forces during rotation. The sealing performance of labyrinth seals may be enhanced by engaging them with a honeycomb-like material, e.g., attached to an adjacent stationary surface, that provides an abradable mating surface to the moving teeth. Similar applications also apply to so-called knife edge seals.
Radial and/or axial excursions of such seals usually cause a non-recovering groove to develop in the engaged honeycomb material that eventually allows air, gases, etc. to escape past the seal when it is not fully engaged with the groove. Also, with such axial or radial motion, this “rub groove” may position in a different alignment from where the seal positions in a normal operating or “steady state” condition. Seal clearance variation usually also occurs in such seals during radial or axial excursions, which causes inconsistent leakage flow during various operating conditions.